The present invention relates to a device and a method determining a characteristic value of a magnetic switch valve by electrical means.
A magnetic switch valve is opened by means of a switch magnet to which current is applied moving a movable switch element (rotor) against a restoring force. The valve is closed again by interrupting the application of current to the switch magnet. The rotor then falls back to the initial position thereof.
Particularly in the case of fast switching valves of this kind, it is necessary to precisely set the switching path of the rotor. The control speed and the robustness of the valves can only be simultaneously optimized by a precise setting of the switching path. Control speed and robustness have opposite requirements: mechanical switching paths that are as small as possible are necessary for high control speed, wherein a certain minimum switching path my not be undershot in order to prevent throttling effects. The speed, with which the rotor returns when closing the valve into the initial position thereof also increases when the switching path increases. Upon reaching the end position large forces now act which can damage the sealing surface of the valve. On the other hand, a large switching path makes the valve robust against effects which reduce the switching path, for example deposits and coatings. Furthermore, the flow volume increases with an increasing switching path in the open state of the valve.
The basis for each optimization of the switching path is that said switching path is known. The rotor is however not accessible for a mechanical or optical measurement of the switching path in the operationally ready state of the valve. The problem is circumvented by estimating the switching path from the time that it takes the switch valve to move from the one to the other end position or by measuring the magnetic flux. The estimation from the time measurement can be strongly distorted by friction or hydraulic tackiness. In order to be able to infer the switching path from the measurement of the magnetic flux, detailed knowledge of the magnetic circuit and the rotor is necessary.
Further important characteristic values, which change with longer use of a valve and therefore should be monitored, are the spring constants of the restoring force and the friction coefficient effective during the valve actuation. These characteristic values also are not accessible to date by any sufficiently precise measurement in the operationally ready state of the valve.